The invention relates to a printer, in particular a printer of a tachograph for a motor vehicle, having a housing, a printing unit, a media unit for accommodating the medium which is to be printed, which media unit has a carrier and can be moved jointly with the carrier, relative to the printing unit, in a push-in direction into an operating position and counter to the push-in direction out of an operating position, and can be moved at least partly out of the housing, and the carrier has lateral first guide elements, in the manner of a drawer, which interact with second guide elements in such a way that the carrier can be moved in the push-in direction and counter to the push-in direction out of the housing.
An apparatus of this type is already known from German utility model 299 20 901.6 which deals with a tachograph of flat, parallelepiped-shaped design. The thermal printing head and the transport roller for the transport of the printing medium which is present as a tape spool can be separated spatially from one another by moving the carrier out of the housing of the printing apparatus. This arrangement is based on the need for it to be possible to change or refill the printing medium simply and with a small amount of manual maneuvers, without it being necessary to handle the sensitive and complicated mechanics of the transport unit for the printing medium and of the printing unit.
However, the technical implementation of this inventive idea has proved problematical in the past. If the transport module for the printing medium and the printing module are separated from one another during opening of the housing for changing the printing medium or the paper roll and are subsequently reconnected to one another, an only slightly changed position of the moved transport unit still has a negative effect on the printed result. On account of the bearing play required solely for the movability of the transport unit, an exact reproduction of the position of the transport unit relative to the printing unit is an aim which runs counter to the requirement for displaceability of the transport unit. The disadvantages of the prior art and the problems are increased additionally by the customary component tolerances which are already fixed from economic aspects. In conjunction with the fixed component tolerances, the movement play which is definitely required for the transport unit leads to unacceptable print quality results.
The German published document DE 40 05 810 A1 has already disclosed a thermal transfer printing apparatus, in which changing of the media is extremely complicated for the user on account of the need to thread in the endless medium which is to be printed. The European patent application EP 1 103 927 A2 discloses a tachograph having an integrated printing apparatus, it being possible for the printing apparatus, jointly with the storage trough for the printing medium, to be pulled out of the tachograph in the manner of a drawer for changing the media. However, the media change is comparatively complicated here, as the printing medium has to be threaded into the front part of the drawer. The arrangement of a printing unit with respect to a media unit in the housing of a tachograph, which arrangement is proposed in the international patent application WO 02/063571 A1, makes a simpler media change possible, it being possible for the media unit to be moved relative to the printing unit in the manner of a drawer and in a manner which can be pulled out of the housing. However, this arrangement requires very high precision of the drawer-like guide for the media unit, in order to achieve the required print quality.
Proceeding from the problems and disadvantages of the prior art, the invention has been based on the object of providing a printer, the media unit of which printer can be moved relative to the printing unit for accommodating the medium to be printed, and which printer at the same time produces a printed image of convincing quality.